This code is the same for all architectures with the following invariants:

- arm gurantees irqs are disabled when calling irq_exit so it can call
  __do_softirq directly instead of do_softirq

- arm26 is totally broken for about half a year, I didn't care for it

- some architectures use softirq_pending(smp_processor_id()) instead of
  local_softirq_pending, but they always evaluate to the same

This patch moves the out of line irq_exit implementation from
kernel/irq/handle.c which depends on CONFIG_GENERIC_HARDIRQS to
kernel/softirq.c which is always compiled, tweaks it for the arm special
case and moves the irq_enter/irq_exit/nmi_enter/nmi_exit bits from
asm-*/hardirq.h to linux/hardirq.h
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>